This invention relates, generally, to the production of thin film and, more particularly, to the detection of breaks or slack conditions in a continuously advancing web or film.
In existing machines, film is produced by extruding a web of molten, polymeric, film-forming materials onto a quench wheel and then advancing the web, under tension, through stretching and slitting stations to one or more windups. In the event of a break and/or a loss of tension, extrusion continues which means that the web must be cut and diverted to waste until the malfunction has been remedied. Reflective photocells have been used to detect discontinuities but are neither reliable not suitable in environments that are either corrosive or explosive. Furthermore, in enclosures for the stretching stations of a film-producing machine, contaminants such as escaping monomers can cloud the photocells and thereby disable the monitoring process.